In recent years, in the manufacturing industry of liquid crystal displays, with the demand for liquid crystal panels become increasingly greater, the requirement for the convey efficiency of the automated material conveying system in the production process is also continuously promoted. In an automated material conveying system, conveying tools, mainly the storage/retrieval machines, are used to convey the cartridges carrying the display panels. Hence, the convey efficiency of the storage/retrieval machine has direct influence upon the efficiency of the automated conveying system, and also has indirect influence upon the supply volume of the entire liquid crystal industry.
FIG. 1 is a schematic view illustrating the overall structure of a traditional storage/retrieval machine; and FIG. 2 is a structural schematic view of the fork assembly for the traditional storage/retrieval machine. The configuration of the traditional storage/retrieval machine comprises a walking unit 1 on which a main frame 2 is provided, the main frame 2 is provided with a lifting unit 3 therein, a lifting unit 3 is connected with a transfer table 5 and can bring the transfer table 5 to move up and down, and the transfer table 5 is equipped with a fork assembly 4. The fork assembly 4 comprises a rotating table 41 which is arranged on the transfer table 5. The rotating table 41 is provided with two rotary motors 421, and each rotary motor 421 is connected with an extension arm 43 comprising a first arm 431, a second arm 432 and a third arm 433. The two rotary motors 421 are each connected with one first arm 431, and the rotary motor 421 can bring the first arm 431 to rotate horizontally. The outer ends of the two first arms 431 are each hinged with one second arm 432, and the outer ends of the two second arms 432 are hinged horizontally with the same third arm 433. The storage/retrieval machine further comprises a control system (not illustrated in the drawing) which is used for control the integral operation of the storage/retrieval machine.
The extension stroke of the extension arm 43 can be determined in the following manner. Two sensors are provided on the fork assembly 4: one sensor is used for determining the minimum distance point to which the extension arm 43 can extend, called the minimum distance point position sensor 44, and the other sensor is used for determining the maximum distance point to which the extension arm 43 can extend, called the maximum distance point position sensor 45. Both sensors 44, 45 are coupled with the control system. When the extension arm 43 moves to the minimum distance point position, the minimum distance point position sensor 44 may send signal to the control system, and the control system limits the extension arm 43 at the minimum distance point position; when the extension arm 43 moves to the maximum distance point position, the maximum distance point position sensor 45 may send signal to the control system, and the control system limits the extension arm 43 at the maximum distance point position.
However, when the aforesaid traditional storage/retrieval machine is used for conveying cartridges, the extension arm frequently performs protruding or receding actions in the process of taking and placing the cartridges, and for each of the protruding and receding actions, the extension arm will have to pass through the entire stroke between the minimum distance point and the maximum distance point, resulting in a time-consuming telescoping process for the extension arm assembly, which reduces the convey efficiency of the storage/retrieval machine.